DeNOx Catalysts Research Articles

Effect of crystalline TiO2 on V2O5WO3/TiO2 as tunable low-temperature shift De-NOx catalyst

Based on the crystalline size of anatase TiO2, a series of tunable low-temperature shift V2O5-WO3/TiO2 (VW/Ti) catalysts for NH3 selective catalytic reduction (NH3-SCR) of NOx were prepared by impregnation process. These catalysts contained a loading amount of 2 wt% WO3 and either 2 or 5 wt% V2O5. The tunable low-temperature shift De-NOx performance of the VW/Ti catalysts was significantly enhanced and dramatically decreased after heat treatment of TiO2 from 100 °C to 700 °C (Ti100–Ti700). Nearly 100 % De-NOx efficiency was achieved at a gas hourly space velocity (GHSV) of 60,000 h−1. A notable shift from higher to lower temperatures was observed from V2W2/Ti100 to V2W2/Ti600; however, the activity was lost for V2W2/Ti650 to V2W2/Ti700. When the V2O5 loading increased from 2 wt% to 5 wt%, the V5W2/Ti600 showed the highest De-NOx efficiency at 225 °C, demonstrating a remarkable synergistic effect compared to the V2W2/Ti100 catalyst, which achieved maximum efficiency at 375 °C. The De-NOx performance and low-temperature shift effect of these catalysts were elucidated by considering TiO2 crystalline size, the synergistic effect between V2O5 content and TiO2, and the V4+/V5+ oxidation state of V2O5 in the catalyst. Additionally, the high crystalline TiO2-based V2W2/Ti600 catalyst prepared in this study is expected to effectively decompose NOx at low temperatures, in contrast to the low crystalline TiO2-based V2W2/Ti100 catalyst.

Study on N2 selectivity of iron-manganese ore catalysts in NH3-SCR process

Natural iron-manganese ores exhibit a good deNOx activity at low temperatures after a simple treatment, but the reason for its low N2 selectivity requires further in-depth study. This work conducted deNOx performance and characterization tests on iron-manganese ore catalysts. Based on the experimental results, a simplified computational model of the iron-manganese ore catalyst (Fe2O3/MnO2 (110) surface) was constructed, and the density functional theory (DFT) method was used to investigate the mechanism of N2 formation in the NH3-SCR process. Fe and Mn in the iron-manganese ore play an important role in the deNOx activity, and NH3 forms the stable chemical adsorption on its surface, especially on the Fe site, where the adsorption capacity of NH3 is stronger than that of Mn site. The Fe site exhibits better ability than the Mn site in the dehydrogenation reaction of NH3. However, in a comprehensive comparison, the capability of iron-manganese ore catalyst to promote NH3 dehydrogenation is not high. In addition, the key NH2NO intermediate prefers to form on the Mn site over the Fe2O3/MnO2 (110) surface. Among them, the Mn site is better than the Fe site in promoting the decomposition of NH2NO intermediate to form N2. The study can further understand the microscopic mechanism of iron-manganese ore catalysts in N2 formation, which lays a foundation for improving the N2 selectivity of iron-manganese ore deNOx catalysts.

Particulate removal characteristics of commercial-scale DeNOx catalyst cartridge coupled filter bags

The commercial-scale DeNOx catalyst cartridge coupled with filter bag have been developed for the removal of fine particulate matter and nitrogen oxides (NOx) in flue gases. The DeNOx catalyst cartridge coupled filter bag is made up of a microporous PTFE (polytetrafluoroethylene) membrane/impregnated polyimide fiber needle-punched pleated filter bag designed for the removal of ultrafine particulates, along with a pellet selective catalytic reduction catalyst-filled cartridge for the removal of NOx. V2O5-MoO3/TiO2 catalyst was used as the DeNOx catalyst. The distribution of cleaning air velocity inside the DeNOx catalyst cartridge-coupled filter bag, which is injected with compressed air from the high-volume low-pressure (HVLP) pulse injector to remove the deposited dust cake from the surface of the filter bags during pulse-jet cleaning, was confirmed using computational fluid dynamics (CFD). The particulate removal and dust cake dislodgement characteristics of the DeNOx catalyst cartridge coupled filter bag were tested in a commercial-scale filter bag test unit under conditions simulating fossil fuel combustion flue gas. The commercial-scale DeNOx catalyst cartridge coupled filter bag was 165 mm in diameter, 2000 mm in total length, and contained approximately 12 kg of DeNOx catalyst- filled cartridges. Nine commercial-scale DeNOx catalyst cartridge coupled filter bags were installed in the commercial-scale filter test unit. The experimental conditions were as follows: flue gas temperature 200 °C, flue gas flow rate 3000Nm3/h, NO, SO2, and particulate concentration in inflow flue gas 200 ppm, 7 ppm, and 5000 mg/Nm3 respectively, resulting in different values of filtration velocities. The efficiency of bag cleaning and intervals, overall collection efficiency, fractional efficiency, and filter quality were investigated. The average bag cleaning efficiency and overall collection efficiency were 95.5%, 91.5%, and 83.3% at filtration velocities of 0.8, 1.0 and 1.2 m/min, respectively. The corresponding values for overall collection efficiency were 99.9%, 99.5%, and 98.2%. So, both bag cleaning efficiency and overall collection efficiency decreased with increased filtration velocity. The present study confirmed that DeNOx catalyst cartridge coupled filter bags have relatively higher bag cleaning efficiency, collection efficiency, and filter quality for challenging fossil fuel combustion flue gas. Particularly, the fractional efficiency for micron-sized particles was considerably higher at lower filtration velocities.

Three-dimensionally ordered macroporous CeZrVOx catalyst with remarkable NH3-SCR performance and SO2 tolerance: Key roles of the morphology and highly dispersed V species

Developing effective low-temperature deNOx catalysts with high activity, SO2 tolerance, and stability is crucial yet challenging. Thus, in this work, CeZrVOx catalyst with a three-dimensional ordered macroporous structure was successfully prepared using the PMMA hard template method, and the catalyst has a macropore diameter of up to 110−140 nm. The modification with highly dispersed V significantly enhances the low-temperature activity and broadens the activity temperature window of the catalyst. This is mainly attributed to the increased number of surface acid sites, as well as the higher proportion of Ce3+ and active surface oxygen species induced by V modification. The V species prepared by this method are highly dispersed on the CeZrOx solid solution and combine with Ce to form CeVO4, which is also an important factor in enhancing catalytic activity. The catalyst does not react with SO2 to produce inactive sulfate species; even the formed cerium sulfate species are beneficial for high-temperature performance. More importantly, due to its unique interconnected three-dimensional ordered structure, the catalyst can significantly inhibit the blockage and coverage of NH4HSO4 on the catalyst, thereby exhibiting remarkable resistance to physical poisoning caused by SO2. Even in high concentrations of sulfur-containing atmospheres, the catalyst still shows high catalytic activity. This work offers meaningful guidance into developing denitration catalysts that show superior performance and robust resistance to both physical and chemical poisoning induced by SO2.

Enhanced DeNOx catalysis: Induction-heating-catalysis-ready 3D stable Ni supported metal combinations

Catalysis plays a critical role in the quest for sustainable automotive technology, particularly in reducing harmful emissions from vehicles. The catalysts are required to operate efficiently in dynamic and challenging environments. This study introduces innovative deNOx catalysts featuring nominal concentrations of Pd and Re nanoparticles doped on a NiMo support. The best-performing fabricated catalyst demonstrated impressive 95 % NOx conversion at 250°C, significantly outperforming traditional systems and reducing ammonia slip. Integrating nickel as the support material was strategic choice to leverage novel induction heating-assisted catalytic system. This approach is particularly advantageous when starting cold engine, reducing harmful NOx emissions when the catalyst is not fully operational. Functional monolith model of car converter catalyst with similar composition was also developed. This research presents novel catalyst solution that achieves high deNOx efficiency while offering a cost-effective alternative to traditional methods. Induction heating enhances the catalyst's performance, particularly at lower temperatures, showcasing significant improvement over conventional thermal methods.

New insights into the effects of Nd on low-temperature hydrothermal stability of deNOx Cu/SAPO-34 catalysts: A comparative evaluation of the mechanism

Designing a highly efficient and cost-effective deNOx catalyst for curbing NOx emission in diesel vehicle exhaust is highly desired but challenging. Herin, a Nd-promoted Cu/SAPO-34 (Cu/Nd-S) catalyst with superior NOx reduction efficiency and low-temperature hydrothermal stability was proposed. The NOx conversion of fresh Cu/Nd-S-F at 200 °C was improved to 86.1 % compared to fresh Cu/S-F (78.1 %). XRD and H2-TPR results revealed that Nd3+ ions filled the defect sites of zeolites and combined with P species to form NdPO4, thus stabilizing the zeolite framework and maintaining the stability of active copper species. The interaction between Nd3+ ions and Cu2+ ions protected the active copper species (Cu2+-2Z and [Cu(OH)]+-Z) from the attack of low-temperature (70 °C) moisture. However, Cu/SAPO-34 suffered from the rapid and irreversible deterioration under 70 °C of water bath, leading to the loss of surface Brønsted acid sites (Al-(OH)-Si) and isolated Cu2+ ions, so aged Cu/S-70 exhibited inferior NOx conversion. Meanwhile, in situ DRIFTS transient experiments elaborated that the NH3-SCR reaction over Cu/SAPO-34 and Cu/Nd-SAPO-34 catalysts obeyed the E-R and L-H routes simultaneously. To be noted, the Nd-doping engineering afforded a promising strategy for boosting the low-temperature hydrothermal stability of Cu/SAPO-34 catalysts for the practical application of NOx removal.

Unlocking Mixed-Metal Oxides Active Centers via Acidity Regulation for K&SO2 Poisoning Resistance: Self-Detoxification Mechanism of Zeolite-Confined deNOx Catalysts.

Selective catalytic reduction of nitrogen oxides (NOx) with ammonia (NH3-SCR) is an efficient NOx reduction strategy, while the denitrification (deNOx) catalysts suffer from serious deactivation due to the coexistence of multiple poisoning substances, such as alkali metal (e.g., K), SO2, etc., in industrial flue gases. It is essential to understand the interaction among various poisons and their effects on the deNOx process. Herein, the ZSM-5 zeolite-confined MnSmOx mixed (MnSmOx@ZSM-5) catalyst exhibited better deNOx performance after the poisoning of K, SO2, and/or K&SO2 than the MnSmOx and MnSmOx/ZSM-5 catalysts, the deNOx activity of which at high temperature (H-T) increased significantly (>90% NOx conversion in the range of 220-480 °C). It has been demonstrated that K would occupy both redox and acidic sites, which severely reduced the reactivity of MnSmOx/ZSM-5 catalysts. The most important, K element is preferentially deposited at -OH on the surface of ZSM-5 carrier due to the electrostatic attraction (-O-K). As for the K&SO2 poisoning catalyst, SO2 preferred to be combined with the surface-deposited K (-O-K-SO2ads) according to XPS and density functional theory (DFT) results, the poisoned active sites by K would be released. The K migration behavior was induced by SO2 over K-poisoned MnSmOx@ZSM-5 catalysts, and the balance of surface redox and acidic site was regulated, like a synergistic promoter, which led to K-poisoning buffering and activity recovery. This work contributes to the understanding of the self-detoxification interaction between alkali metals (e.g., K) and SO2 on deNOx catalysts and provides a novel strategy for the adaptive use of one poisoning substance to counter another for practical NOx reduction.

High-temperature selective reduction of NOx into N2 catalyzed by different ion-doped titania

The active titanium-based composite oxide carrier with strong thermal stability and surface acidity is the key to ensure the steady operation of high-temperature deNOx catalyst for gas-fired exhaust. In this paper, W6+, Zr4+, Mo6+, Al3+, Si4+, Cu2+, Co2+, Mn2+, Fe3+ doped titanium-based composite oxides were synthesized by sol–gel method. The effects of ion species, doping amount, calcination temperature on NH3-SCR deNOx efficiency and resistance to water vapor and SO2 poisoning were investigated. Results showed that the Cu2+, Co2+, Mn2+, Fe3+ doped titanium-based composite oxides calcined at 630 °C had negligible deNOx activity, while the doping of W6+, Zr4+, Mo6+, Al3+ and Si4+ improved the NH3-SCR activity and anti-water vapor and SO2 poisoning of titanium-based composite oxide. The deNOx efficiency of the best compatibility of the five ions doping was TiW0.1Ox-630 > TiMo0.12Ox-630 > TiAl0.11Ox-487 > TiZr0.06Ox-538 ≈ TiSi0.04Ox-582, which was consistent with the order of total acid amount. The order of resistance to water vapor and SO2 poisoning and resistance to high temperature thermal shock was TiW0.1Ox-630 ≈ TiMo0.12Ox-630 > TiSi0.04Ox-582 > TiZr0.06Ox-538 > TiAl0.11Ox-487. Doping of five ions inhibited the transformation of anatase TiO2 to rutile TiO2 in different degrees. Among them, W6+ doping had the best inhibitory effect and the exposure ratio of TiO2 (101) crystal plane in TiW0.1Ox-630 was the highest, which was beneficial to NH3-SCR of NOx. Furthermore, the concentration of chemisorbed oxygen Oα was in the order of TiW0.1Ox-630 > TiMo0.12Ox-630 > TiAl0.11Ox-487 > TiZr0.06Ox-538 > TiSi0.04Ox-582. The higher the concentration of Oα is, the more conducive to the oxidation of NO to NO2 and the promotion of NH3 adsorption and dehydrogenation oxidation.

Collaborative optimization of de-NOx & NH4HSO4 decomposition over Cu-based LDO catalysts: Perspective from the acidic and redox properties

Low temperature de-NOx catalyst with excellent resistance to ammonium bisulfate (ABS) is of great practical significance. Study about the simultaneous optimization of de-NOx performance and ABS resistance by acidic and redox properties regulation is imperative. In this work, the influence of the acidic and redox properties to the de-NOx & ABS decomposition performance was investigated via three Cu-based LDO model catalysts with distinct surface chemical character. Test results indicated that the low temperature de-NOx performance of both the modified Cu2NiAl-LDO and Cu2CoAl-LDO catalysts was slightly improved, while their in situ ABS resistance behavior was remarkably different (Cu2CoAl-LDO > Cu3Al-LDO > Cu2NiAl-LDO). TPDC and TPSR test evidenced that the ABS thermal decomposition or its reactivity with NOx was facilitated over Cu2CoAl-LDO catalyst, but inhibited over Cu2NiAl-LDO catalyst. Characterizations revealed the Cu2CoAl-LDO catalyst with stronger redox property could contribute to ABS decomposition, while more weak acid sites on Cu2NiAl-LDO catalyst induced a negative effect for ABS decomposition. Our study might provide guidance on the rational design of de-NOx & anti-ABS catalysts for future studies.

Heteroatoms doped iron oxide-based catalyst prepared from zinc slag for efficient selective catalytic reduction of NOx with NH3

Excessive emissions of nitrogen oxides from flue gas have imposed various detrimental impacts on environment, and the development of deNOx catalysts with low-cost and high performance is an urgent requirement. Iron oxide-based material has been explored for promising deNOx catalysts. However, the unsatisfactory low-temperature activity limits their practical applications. In this study, a series of excellent low-temperature denitrification catalysts (Ha-FeOx/yZS) were prepared by acid treatment of zinc slag, and the mass ratios of Fe to impure ions was regulated by adjusting the acid concentrations. Ha-FeOx/yZS showed high denitrification performance (> 90%) in the range of 180–300 °C, and the optimal NO conversion and N2 selectivity were higher than 95% at 250 °C. Among them, the Ha-FeOx/2ZS synthesized with 2 mol/L HNO3 exhibited the widest temperature window (175–350 °C). The excellent denitrification performance of Ha-FeOx/yZS was mainly attributed to the strong interaction between Fe and impurity ions to inhibit the growth of crystals, making Ha-FeOx/yZS with amorphous structure, nice fine particles, large specific surface area, more surface acid sites and high chemisorbed oxygen. The in-situ DRIFT experiments confirmed that the SCR reaction on the Ha-FeOx/yZS followed both Langmuir-Hinshelwood (L-H) mechanism and Eley-Rideal (E-R) mechanism. The present work proposed a high value-added method for the preparation of cost-effective catalysts from zinc slag, which showed a promising application prospect in NOx removal by selective catalytic reduction with ammonia.

Discovering the remarkable deNOx activity and anti-K poisoning of MnFeOx/H-Beta composite catalyst

The practical application of MnFeOx catalyst is limited due to its narrow temperature window and poor resistance to alkali metal poisoning, such as K and Na. Alkali metal poisoning has always been a major factor in the deactivation of fixed-source denitration (deNOx) catalysts. Despite high activity at around 200 °C , the catalyst's susceptibility to alkali metal poisoning hinders its effectiveness. In this study, a novel MnFeOx/H-Beta composite catalyst was prepared by the simple wet impregnation method. Beta zeolite, known for its large specific surface area compared to MnFeOx, special twelve-membered ring channel, and abundant acid sites, was introduced to adjust the acid and redox active sites. This resulted in MnFeOx/H-Beta having a wider temperature window and excellent resistance to K poisoning. Notably, the NOx conversion rate exceeded 80% between 180 and 460 °C . K poisoning significantly reduces the acidity of the catalyst, as confirmed by various characterizations such as NH3-TPD and NH3 adsorption in situ DRIFTs. After K poisoning, the total acid content of MnFeOx/H-Beta decreased from 14.99 to 9.47 mmol g−1. The low acid content of MnFeOx allows the active sites to be easily covered by K, resulting in a reduction of the SCR performance, which can be attributed to the reduction of active nitrate species. The abundant acid sites of MnFeOx/H-Beta act as sacrificial sites and can coordinate with alkali metal K, thereby alleviating the poisoning of the catalyst to some extent. DFT calculations confirmed K binding to Brønsted acid sites on H-Beta zeolite, mitigating the detrimental impact of K on catalyst activity and lifetime. This research offers a pathway for designing efficient and alkali metal-resistant deNOx catalysts for real-world industrial applications.

Insight into the reasons for enhanced NH3-SCR activity and SO2 tolerance of Mn-Co layered oxides

Mn-based catalysts have a fatal flaw in selective catalytic reduction (SCR) of NOx with NH3, which is poor SO2 tolerance. In this work, we successfully fabricated Mn-Co layered double oxides (LDOs) by calcining the Mn-Co layered double hydroxides (LDHs) generated by a hydrothermal method using urea solution. The obtained Mn-Co LDO presents excellent catalytic activity and SO2 tolerance in the SCR reaction of NOx with NH3. The enhanced activity can be attributed to the special surface physicochemical properties endowed by its LDO structure, such as large specific surface area, more exposed active sites, relatively high Mn4+ and Oα/(Oα + Oβ) percentage, good reducibility, and abundant acidic sites. The enhanced SO2 tolerance can be ascribed to the weak adsorption energy of SO2 on Mn-Co LDO, which makes it difficult for SO2 to interact with the active sites. Furthermore, the NH3-SCR of NOx reaction that occurs on the surface of the MnCo-LDO follows both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms. This study shines light on the design of Mn-based de-NOx catalysts with excellent SO2 tolerance.

Low-temperature direct decomposition of NO over Rh/NC-MnFe catalyst: activity, stability and mechanism

As the ideal NO removal technology, the biggest challenge associated with the direct catalytic decomposition of NO is the development of highly active deNOx catalysts at low temperatures.

The chemical nature of SO2 poisoning of Cu-CHA-based SCR catalysts for NOx removal in diesel exhausts

Unveiling how the chemistry of the reaction of [Cu2II(NH3)4O2]2+ with NO changes upon exposure to SO2. The important stage of the NH3-SCR cycle in the Cu-CHA deNOx catalyst is investigated with temperature-programmed reaction with NO, XAS and DRIFTS.

Promoting mechanism of Mn doping on the NH3-SCR reaction over the Fe/γ-Al2O3 catalyst surface

To verify the superiority of Mn-Fe dual-component doped catalysts in terms of deNOx performance, the differences of mechanisms in selective catalytic reduction with ammonia (NH3-SCR) between Fe/γ-Al2O3 and Mn-Fe/γ-Al2O3 catalysts were investigated by using the density functional theory (DFT). On the surface of the Fe/γ-Al2O3 catalyst, the NH2 group generated by NH3 dehydrogenation can react with NO and NO2 to form NH2NO and NH2NO2, respectively. The decomposition process of NH2NO is established as the rate-determining step in the reaction between NH3 and NO, while the rate-determining step in the reaction between NH3 and NO2 is the decomposition of NHNO2. Mn doping significantly enhances the catalyst's adsorption performance for O2 and oxidation ability toward NO, thereby promoting the production of NO2. Additionally, Mn doping markedly reduces the reaction barriers, facilitating the dissociation of NH2NO and NHNO2 on the Mn-Fe/γ-Al2O3 catalysts. These findings may elucidate the reasons of the effective enhancement of deNOx performance in the Mn-doped Fe/γ-Al2O3 catalysts, which establishes a foundation for the subsequent development and application of Mn-Fe bimetallic-doped SCR deNOx catalysts.

Low-temperature selective catalytic reduction of NOx with NH3: Exploring the mechanism of enhancing H2O tolerance through methylation functionalization and structural regulation in IPAx-Mn-BTC

In the selective catalytic reduction (SCR) of NOx with NH3, it is crucial to design low-temperature de-nitrification (de-NOx) catalysts with high H2O tolerance. Here, we developed a type of low-temperature de-NOx catalyst (IPAx-Mn-BTC) with strong H2O tolerance through methyl functionalization. In the presence of the optimal catalyst (IPA50-Mn-BTC), the NOx conversion only decreased from 97% to 90% after introducing 6% H2O for 6 h at low temperature of 150 °C. The results of in-situ DRIFTS and density functional theory calculations confirm that the de-NOx reaction process and the generation of intermediate states that occur on the surface of the IPA50-Mn-BTC are not affected by H2O. The elimination of the small pore size (< 4.3 nm) and the diminished H2O adsorption energy resulted from methyl functionalization are the key factors behind the improved H2O tolerance. This work provides a new approach for designing low-temperature de-NOx catalysts with high H2O tolerance.

The Study of SCR Mechanism on LaMn1−xFexO3 Catalyst Surface Based DFT

Perovskite SCR catalysts have become a hot research topic in the field of de-NOx catalyst development. This article selects LaMnO3 with high performance as the research object, modifies the catalyst by doping some iron elements instead of manganese elements, and applies density functional theory to study its reaction mechanism, providing theoretical reference for further research on perovskite. Research has found that several main reactants such as NH3, NO, and O2 can form stable adsorption at the active site, with NO more inclined to adsorb at the nitrogen atom end at the active site. The oxidation of O2 molecules after adsorption is greater than that of the active site. The adsorption capacity of the Mn active site of the catalyst before modification on the above molecules is weaker than that of the Fe active site introduced after modification. Under both anaerobic and aerobic conditions in the SCR reaction process, NH3 molecules are first adsorbed at the active site, and then influenced by lattice oxygen under anaerobic conditions. Under aerobic conditions, they are gradually dehydrogenated and produce NH2 and NH radicals. These two radicals react with NO molecules to form intermediate products in the form of NH2NO and NHNO molecules. Due to the instability of the intermediate products, they ultimately decompose into N2 and H2O molecules. The introduction of Fe active sites can increase the generation of NH2 and NH radicals during the reaction process and simplify the reaction process between NH2 radicals and NO molecules, which will be conducive to the completion of the reaction.

Probing the Atomistic Reaction Pathways in CuO/C Catalysts.

CuOx/C catalysts have been used in the selective catalytic reduction of NOx because of the exceptional low-temperature denitration (de-NOx) activity. A fundamental understanding of the reaction between CuO and C is critical for controlling the component of CuOx/C and thus optimizing the catalytic performance. In this study, a transmission electron microscope equipped with an in situ heating device was utilized to investigate the atomic-scale reaction between CuO and C. We report two reaction mechanisms relying on the volume ratio between C and CuO: (1) The reduction from CuO to Cu2O (when the ratio is < ∼31%); (2) the reduction of CuO into polycrystalline Cu (when the ratio is > ∼34%). The atomistic reduction pathway can be well interpreted by considering the diffusion of O vacancy through the first-principle calculations. The atomic-scale exploration of CuO/C offers ample prospects for the design of industrial de-NOx catalysts in the future.

Insight into the temperature-dependent SO2 resistance over Mn-based de-NOx catalyst

Herein, two simple model catalysts (Mn3O4 and MnFeOx) were fabricated and operated under different temperatures (100, 150, 200, 250 °C) in SCR atmosphere with the presence of SO2, followed by thermal regeneration and characterizations to reveal the deactivation mechanism and the role of FeOx. The results indicated both catalysts exhibited temperature-dependent deactivation behavior, where the total activity loss displayed volcano-type SO2 resistance tendency within 100–250 °C and the most severe activity loss (98 % for Mn3O4 and 81 % for MnFeOx) was found at 150 °C. Meanwhile, the higher relative proportion of irreversible activity loss was found at lower temperatures, which is associated with the more easily saturated chemical adsorption of SO2 as evidenced by SO2+O2 breakthrough test. At higher temperatures, the SO2 oxidation and its further transformation into NH4HSO4 could be favored, thus resulting in increased reversible activity loss. The FeOx modification can protect MnOx species from sulfation to a certain degree and lower the irreversible deactivation, which is evidenced by the binding energy upshift and downshift of Fen+ species after being poisoned and regenerated, as well as the slightly changed binding energy of Mnn+ species from the XPS analysis.

Improved N2 Selectivity of MnOx Catalysts for NOx Reduction by Engineering Bridged Mn3+ Sites

Mn-based catalysts are promising for selective catalytic reduction (SCR) of NOx with NH3 at low temperatures due to their excellent redox capacity. However, the N2 selectivity of Mn-based catalysts is an urgent problem for practical application owing to excessive oxidizability. To solve this issue, we report a Mn-based catalyst using amorphous ZrTiOx as the support (Mn/ZrTi-A) with both excellent low-temperature NOx conversion and N2 selectivity. It is found that the amorphous structure of ZrTiOx modulates the metal-support interaction for anchoring the highly dispersed active MnOx species and constructs a uniquely bridged Mn3+ bonded with the support through oxygen linked to Ti4+ and Zr4+, respectively, which regulates the optimal oxidizability of the MnOx species. As a result, Mn/ZrTi-A is not conducive to the formation of ammonium nitrate that readily decomposes to N2O, thus further increasing N2 selectivity. This work investigates the role of an amorphous support in promoting the N2 selectivity of a manganese-based catalyst and sheds light on the design of efficient low-temperature deNOx catalysts.